This invention relates to systems and methods for noninvasively and/or continuously and quantitatively measuring spectrophotometrically a patient""s blood urea nitrogen, blood osmolarity, plasma free hemoglobin, and tissue water content.
Modern medical practice utilizes a number of procedures and indicators to assess a patient""s condition. Blood urea nitrogen (xe2x80x9cBUNxe2x80x9d), plasma free hemoglobin (xe2x80x9cPFHxe2x80x9d), and tissue water content are important indications of a patient""s condition.
BUN, which is the amount of urea or urea nitrogen per unit volume of blood expressed, typically, in milligram percent units (mg %) is typically a by-product of the catabolism of various body proteins principally found in muscle and liver tissues. It is present in extra (and intra) vascular spaces, but later processed and excreted through the kidneys into the urine. Specifically, in the case of end-stage renal disease patients, acute renal failure, or chronic renal failure, wherein the kidneys do not function properly to excrete this waste product, the BUN levels elevate. Subsequently, urea becomes a toxin to many other organ systems of the body including the brain, heart, skin, etc.
Medical professionals routinely desire to know the BUN, or dialysate urea or dialysate urea nitrogen (DUN) value, of the patient, because of the above-mentioned deleterious and serious side effects. To determine BUN using any of the techniques available today, it is necessary to draw a sample of blood by veni-puncture. Then, using widely accepted techniques, the sample of blood is subjected to biochemical and enzymatic reactions to determine the level of urea in the blood.
Conventional techniques require that a sample of blood be withdrawn from the patient for in-vitro analysis. Any invasion of the subject to obtain blood is accompanied by the problems of inconvenience, stress, and discomfort imposed upon the subject. The infectious risks are also present when the body is invaded, via needle-skin puncture. Additionally, withdrawing blood also creates certain contamination risks to paramedical professionals. Moreover, even in a setting where obtaining a blood sample does not impose any additional problems, for example during surgery, the available techniques require delay between the time that the sample is drawn and the BUN value is correctly processed. Still further, none of the previously available techniques allow for continuous monitoring of the subjects BUN as would be desirable during hemodialysis treatment procedures or even in intensive care treatment.
Specifically in hemodialysis, recent techniques have been developed to enzymatically determine the BUN level in the dialysate fluid as a marker of what is transpiring in the blood. However, these particular enzymatic techniques are likewise fraught with serious drawbacks, not the least of which is that the technique does not give a continuous measurement of the urea nitrogen even in the dialysate fluid. The enzymatic determination is accomplished by periodic, automated, sampling, wherein the enzymatic compounds and dialysate fluids are mixed and the urea nitrogen level is thereby determined.
Medical professionals routinely desire to know the tissue water (or hydration status) of the patient. For example, in hemodialysis (or in end-stage renal disease) patient tissue water increases dramatically due to the inadequate elimination of water from the interstitial and intravascular spaces, since the kidney no longer correctly functions. Hence, the patients become edematous and their tissue water content increases dramatically. In hemodialysis, the goal of therapy is to remove all of the toxins of the blood and body. Some of these toxins are the urea, potassium, and even water which can become a significant toxin to the patient. Therefore, removal of water from the tissue is crucial because this water overloaded state requires excessive energy expenditure by the heart to function. Hence, many dialysis patients are in a state of pulmonary edema, congestive heart failure, etc., due to the large xe2x80x9cloadxe2x80x9d that the heart must push against. Therefore, to reach an appropriate xe2x80x9cdry weightxe2x80x9d (the patient""s body weight when the kidneys were functioning normally) is an important dialysis therapy goal.
Medical professionals in other specialties are desirous of knowing the tissue water content of non-renal, edematous patients for other reasons. Hormonal imbalances, menstrual cycle variations, congestive heart failure and other causes also result in pulmonary edema and peripheral edema. These states require the knowledge of the interstitial tissue water content.
Tissue water content is conventionally measured by bioelectrical impedance; however, bioimpedance can be costly and requires the injection of small electrical currents into the patient. Another technique involves measuring the amount of water in the tissue spaces by injecting radio-isotopes into a patient. This is done principally on a research basis, however, because of the attendant radiation risks.
PFH (Plasma Free Hemoglobin) is the amount of hemoglobin not contained inside a red blood cell, but rather free in plasma solution and is expressed, typically in milligram percent units (mg %). PFH is typically a result of red blood cell breakage or hemolysis, with spillage of the hemoglobin directly into the plasma. Specifically, in the case of end-stage renal disease patients, acute renal failure, or chronic renal failure, wherein the kidneys do not function properly and hemodialysis is required, the PFH levels in the blood may elevate due to tubing lines kinking and pump rollers crushing the red blood cells during the course of the hemodialysis treatment. This can occur in cardiopulmonary surgeries as well. Subsequently, PFH itself becomes a toxin to many other organ systems of the body.
Medical professionals desire to know the PFH of the patient, because of the above mentioned deleterious and serious side effects associated with the presence of PFH. In conventional techniques, PFH is measured by drawing a sample of blood by veni-puncture. Then, using widely accepted techniques the sample of blood is subjected to biochemical reactions to determine the level of PFH in the plasma of the blood.
Blood osmolarity is the osmolar content of blood per unit volume of blood expressed, typically, in milliosmolar units. The osmolar content of blood (and/or the sodium content) should have a narrow range of values due to the body""s compensatory abilities. However, in the case of end-stage renal disease patients, acute failure, or chronic renal failure, wherein the kidneys do not function properly and hemodialysis is required, the blood osmolarity varies greatly.
Medical professionals routinely desire to know the osmolarity or sodium value of the patient, because of the deleterious and serious side effects associated with levels outside the normal range. To determine the blood osmolarity (OSM) or blood sodium (Na+) content using any of the techniques available today, it is necessary to draw a sample of blood by veni-puncture. Then, using widely accepted techniques the sample of blood is subjected to physical and biochemical reactions to determine the level of OSM or Na+ in the blood.
In view of the drawbacks in the available art dealing with invasive blood constituent determinations, it would be an advance in the art to noninvasively and quantitatively determine a subject""s blood constituent including BUN, PFH, tissue water, osmolarity, and Na+. It would also be an advance to provide a system and method for noninvasive blood constituent monitoring which utilizes electromagnetic emissions as the information carrier for information relating to BUN, PFH, tissue water, osmolarity, and Na+.
It is an object of the present invention to provide a method and system for noninvasively measuring and monitoring tissue water.
It is another object of the present invention to provide a method and system for noninvasively measuring and monitoring urea in the blood or dialysate fluid.
It is a further object of the present invention to provide a method and system for noninvasively measuring and monitoring PFH in the blood.
It is yet an object of the present invention to provide a method and system for noninvasively measuring and monitoring osmolarity and Na+ of the blood.
In general, the present invention is directed to apparatus and methods for determining a biologic constituent value, such as BUN, PFH, tissue water and osmolarity, transcutaneously, continuously, and noninvasively.
One aspect of the present invention provides a method and system for the noninvasive measurement of tissue water content in which an emitter and a detector are positioned outside of a patient (either remote from the patient or, preferably, mounted on the skin of a patient), light from the emitter passes through a portion of a patient""s body and is received by the detector. The detector measures light of a selected wavelength that is absorbed by water. The intensity of light at an initial time is measured by a detector; then at a later time, typically after a period of dialysis, the intensity of detected light is compared with the initial intensity and the percent change in tissue water is calculated.
In an alternate method, light of at least two selected wavelengths are detected and absorptions due to blood and/or skin tissues are accounted for. Thus a measurement of intensity transmitted (i.e. detected) versus intensity emitted at a wavelength selected for absorption by water allows calculation of the volume percent of water in a patient""s tissue.
Another aspect of the present invention also provides a method and system for the measurement of urea concentration in the blood of a patient by measuring the quantities of light at two wavelengths where the function of the extinction coefficient versus urea concentration at each given wavelength holds BUN information that is different in at least one of curvature, offset, linearity or sign from the other wavelength.
A further aspect of the present invention provides a method and system for measuring osmolarity (or sodium content) of a patient""s blood.
Yet another aspect of the present invention provides a method and system for measuring plasma free hemoglobin through an optical technique.